The In reality, the terms '''MTA''', '''MDA''', '''MUA''', '''LDA ''' can actually be considered misleading since some of those services can be incorporate together for certain applications, while others can operate as separate entities. are not 100% well defined, because few of the related services are simple and do exactly one thing. There is overlap, so if you don't find the acronyms helpful - don't worry about them. But they can help organize your thoughts when trying to keep all this in your head.